In recent years, demands for thin display devices such as a color liquid crystal display device have been dramatically increased. With the increased demands, higher display quality has been strongly desired. Such a display device includes a color filter in which color layers of three primary colors, i.e., red (R), green (G) and blue (B) are arranged in a predetermined pattern. Therefore, in order to improve display quality, it is essential to fabricate the color filters with high accuracy.
As methods for fabricating the color filter, in general, a staining method, an inkjet method, a printing method, a photolithography method and the like have been known. Among such known color filter fabrication methods, photolithography is currently a mainstream because the number of process steps is relatively small and high controllability and resolution can be achieved.
In photolithography, a color resist is applied to a substrate to form a color layer, and then the color layer is exposed to light through a photomask. Thereafter, the exposed color resist is developed to form a color layer each having a predetermined pattern. Thus, a color filter is fabricated.
If a foreign material is mixed in the color filter, the foreign material itself intercepts display light or the foreign material protrudes into a display medium such as a liquid crystal layer to give an adverse effect to display quality. Therefore, the color filter fabrication process steps are performed in a very clean environment with special attention to prevent mixture of a foreign material into the color layer. However, mixture of a foreign material into the color layer can not be completely prevented.
Moreover, there might be cases where part of the color layer is peeled during fabrication process steps and defective part is created. In such a case, light transmitted through the defective part is not colored and output from a light source as it is. Thus, the light transmitted through the defective part is observed as light leakage.
To cope with this problem, then, it is conventionally known that the inspection step of inspecting for the existence of mixture of a foreign material and defective part is performed to a manufactured color filter. For example, as shown in FIG. 5, a method in which white light is entered in a color filter and an inspector observes transmitted light for inspection is known.
Specifically, in the inspection method, a color filter 103 is disposed so as to be located between an inspector 101 and a light source 102 for outputting white light. In the color filter 103, color layers 103r of R, color layers 103g of G and color layers 103b of B are formed. The color layers 103r transmits only red light in a predetermined wavelength range of incident white light therethrough and output the red light to the inspector side. In the same manner, the color layers 103g transmits only green light through and the color layers 103b transmits only blue light therethrough. If the existence of mixture of a foreign material, defective part or the like is found in any one of the color layers 103r, 103g and 103b, the existence of the foreign material, defective part or the like is observed as abnormal output light by the inspector 101.
However, in the above-described inspection method, light outgoes simultaneously from each of a plurality of color layers 103r, 103g and 103b, and therefore, for example, even if defective part is created in one of the color layers 103r of R and outgoing light from the color layer 103r is changed, it is difficult to accurately and speedily distinguish the change in the outgoing light from the specific color layer. Accordingly, an enormous time is required for reliable inspection, thus resulting in increase in production cost.
As shown in FIG. 6, it is known to dispose an inspection filter 105 between the color filter 103 and the inspector 101 in the above-described inspection method (see, for example, Patent Reference 1). The inspection filter 105 is formed so as to transmit light in a predetermined wavelength range therethrough and largely cuts light transmitted through normal part of the red, green, and blue color layers. On the other hand, light transmitted through the defective part has the whole wavelength range of visible light and the ratio of light being cut by the inspection filter 105 can be reduced. Thus, the contrast between light transmitted through the normal part and light transmitted through the defective part 106 is increased, so that inspection for the defective part 106 can be performed in a simple manner.
(Patent Reference 1) Japanese Laid-Open Publication No. 5-99787